Inherited Carboniferous to Permian zircons constrain the continuity of the Gondwanan continental arc beneath the central Chilean Andes (32-34° S)

Abstract

This study investigates the crustal architecture and tectonomagmatic evolution of the central Chilean Andes (32-34° S) through new U-Pb zircon geochronology. Results from the western border of the Principal Cordillera (32-33° S) reveal a dominant late Carboniferous to early Permian inherited signature, accounting for 60-62% of zircon populations in Late Cretaceous and Miocene units. The high frequency of these Paleozoic ages confirms an unexposed crustal basement, while their incorporation into younger magmas is attributed to the Pocuro Fault system, interpreted as the northern extension of the deep-seated West Andean Thrust (WAT), acting as a conduit for crustal material at least for the Miocene intrusive rocks. Notably, the near-total absence of Mesoproterozoic (Grenvillian) inheritance in these samples suggests that the Cuyania and Chilenia blocks (Grenvillian basement) do not constitute the immediate basement at these latitudes. In the Coastal Cordillera (34° S), the Pailimo Unit yielded a primary magmatic age of 299.2±1.6 Ma without older inherited components, aligning with the entire magmatic belt of south-central Chile (33-40° S). Collectively, these data indicate that the Gondwanan magmatic arc forms a laterally contiguous lithospheric framework extending from the Coastal to the Frontal Cordilleras. This research highlights a major geodynamic transition from a Paleozoic subduction-accretion system toward a mature Andean-type margin. The results underscore the necessity for further integrated studies along the western Gondwana margin.